Generally the air-conditioning and ventilation system of a motor vehicle includes a control panel provided with a plurality of rotary switches arranged on a board. These rotary switches are designed to control different functions, in particular the heating temperature, the fan speed, the orientation of the airflows blown into the passenger space of the vehicle by manipulating a rotary knob. Each rotary switch is at least partially surrounded by a peripheral display zone comprising symbols linked to the controlled functions and identifying different angular positions of the rotary switch.
For practical and aesthetic reasons, a back-lighting device is provided to permit the illumination of each rotary switch, in particular the illumination of the pointer which is arranged on the knob and which marks the angular position of the rotary switch, as well as the illumination of the peripheral display zone.
To increase the number of functions controlled by the same control device, provision is often made to arrange at the centre of the rotary switch one or more push-buttons which also include a back-lighting device.
Currently, to form such a type of rotary switch including at least one push-button at its centre, a tubular rotary encoder is used which is mounted on the board and which provides both an electrical switching function and a haptic, or force-feedback (“feeling”) function. The haptic function in particular allows the user to identify a defined number of angular positions in the form of indexing notches.
A disadvantage of this type of rotary switch is that its diameter is restricted, since it depends on the rotary encoder selected. The same is true of the haptic function which is determined at the design stage by the manufacturer of the rotary encoder. This type of rotary switch does not therefore allow the designer of the control panel to adapt the diameter and the haptic function to particular requirements of the constructor of the vehicle.
Regarding the back-lighting device, the current solutions generally require a large number of electroluminescent diodes (“LEDs”), a part of these being arranged under the symbols of the peripheral display zone, while another part is arranged under the rotary switch, at different angular positions, to illuminate the illuminated pointer in its different angular positions. These solutions are not completely satisfactory as they present problems of the space they occupy on the board and problems of overheating due to the thermal energy produced by the large number of light sources. In particular, the back-lighting of the illuminated pointer and of the illuminated tell-tale with which the push-button at the centre of the rotary switch is provided is very difficult to integrate due to the small amount of space available at the centre and under the rotary switch.